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Tag: testing
September 15, 2020
Pooled Testing for Surveillance of SARS-CoV-2 in Asymptomatic Individuals
A 10-specimen manual pooling algorithm was the optimal pool size for surveillance of asymptomatic healthcare workers. Das et al. found that pool sizes up to 10 were able to detect positive samples with a threshold of cycle time (Ct) <36. An evaluation of this approach included 700 pools (7,000 total samples) and found eight positive…
Characteristics of COVID-19 in Homeless Shelters
Contact tracing events (“surge testing”) identified a much larger proportion of the positive SARS-CoV-2 cases among residents and staff in homeless shelters across King County (Washington State) compared to routine surveillance. Among 29 SARS-CoV-2 positive cases identified from 1,434 encounters of shelter residents and staff in homeless shelters, 72% of cases were detected during “surge…
September 14, 2020
Genome Sequencing of Sewage Detects Regionally Prevalent SARS-CoV-2 Variants
[Preprint, not peer-reviewed] Genome sequencing of SARS-CoV-2 in sewage samples from the San Francisco Bay Area found that the dominant genotypes matched genotypes found in clinical samples from the region. Genotypic variants found in wastewater samples were more similar to local California patient-derived genotypes than they were to those from other regions within the US…
September 10, 2020
High Seroprevalence of Anti-SARS-CoV-2 Antibodies in Chelsea, Massachusetts
• Among asymptomatic residents of Chelsea, Massachusetts without a prior positive PCR test for SARS-CoV-2 (n=200), the seroprevalence of SARS-CoV-2 antibodies was 32% (18% IgM+IgG+, 9% IgM+IgG-, and 5% IgM-IgG+), representing a substantial burden of undocumented infection. Additionally, 51% of participants reported no symptoms in the preceding 4 weeks, of whom 25% (25/101) were seropositive, and…
September 4, 2020
A Direct Comparison of Enhanced Saliva to Nasopharyngeal Swab for the Detection of SARS-CoV-2 in Symptomatic Patients
There was very high agreement in SARS-CoV-2 RT-PCR testing results between enhanced saliva specimens (i.e. strong sniff, elicited cough, and a collection of saliva/secretions) and nasopharyngeal swabs collected from 224 patients suspected of having COVID-19. The positive agreement was 100% and the negative agreement was 99.4%. Saliva samples had a lower mean viral load compared…
September 2, 2020
Analyzing Inherent Biases in SARS-CoV-2 PCR and Serological Epidemiologic Metrics
[Preprint, not peer reviewed] A modeling study found that the observed peak in PCR-detected SARS-CoV-2 infections can follow the peak of true infection incidence due to prolonged shedding of SARS-CoV-2 by approximately ten days in a scenario with an R0 of 1.6 versus 5 days when R0 is 3. Half of those who tested positive…
September 1, 2020
A Simple Approach to Optimum Pool Size for Pooled SARS-CoV-2 Testing
In determining the optimal sample pooling size for large-scale SARS-CoV-2 testing, Regen et al. found that sample pooling only marginally improves testing capacities in high prevalence settings (>10%) while potentially substantially reducing costs and saving labor in low prevalence settings. The investigators derived a simple-to-use formula for calculating the optimal pool size given a target…
Frequency of Serological Non-Responders and False-Negative RT-PCR Results in SARS-CoV-2 Testing: A Population-Based Study
RT-PCR results at first clinical presentation and follow-up serology results were found to differ in about in 15% of patients suffering from nonsevere COVID-19 who had a positive test by RT-PCR and/or subsequent antibody testing. A study from Liechtenstein and Switzerland found that 12 (18%) out of 66 patients with an initial negative RT-PCR test…
August 31, 2020
Saliva or Nasopharyngeal Swab Specimens for Detection of SARS-CoV-2
Wyllie et al. found that self-collected saliva specimens have similar sensitivity to clinician-collected nasopharyngeal specimens for the detection of SARS-CoV-2 during hospitalization. At 1 to 5 days after diagnosis by RT-PCR testing on nasopharyngeal swabs (n=70), 81% of the saliva samples were positive, compared to 71% of the nasopharyngeal swab samples. Wyllie et al. (Aug…
Low Utility of Repeat Real-Time PCR Testing for SARS-CoV-2 in Clinical Specimens
Among people retested for SARS-CoV-2 by RT-PCR within 7-days of a negative test (n=1,113), 2% had a positive result. Challener et al. conclude that the decision to repeat a SARS-CoV-2 PCR should involve the revised probability of COVID-19 based on the initial negative test, an assessment of whether an alternate specimen type may provide a…
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